•−•  ••−•    −•−•  •−  ••−•  •
RF Cafe Morse Code >Hear It<

Job Board

About RF Cafe™

Sitemap

De-embedding lossy transmission line - RF Cafe Forums

Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views. It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if you would like to post something on RF Cafe's Facebook page, please do.

Below are all of the forum threads, including all the responses to the original posts.


alex_shrab
Post subject: De-embedding lossy transmission line Posted: Wed Jul 25, 2007 4:40 pm

Lieutenant


Joined: Wed Jul 25, 2007 4:23 pm
Posts: 1
Hi all experts ,

I'm doing the following experiment:

I have a system which consists of a pair of SMA cables, backplane with microstrip differential pair and another pair of cables which S-parameters I'm trying to find.

Unfortunately, I can't just measure S-parameters of the second pair of cables by using a VNA. But I have S-parameters of the whole system: [SMA cables - backplane - cables], and S-parameters of [SMA cables] and [backplane] separately. The backplane is relatively ‘lossy’ at high frequencies (>10GHz).

I'm converting S-parameters to T-parameters, then taking T[backplane]^-1*T[SMA-cables]^-1*T[whole system]. Then, I’m converting back to S expecting to get "second" cables S matrix. Beyond some frequency (~12GHz), I'm getting very high gain and obviously wrong behavior. I used this technique in the past to de-embed NOT very ‘lossy’ components...
What could be wrong?
Thanks a lot in advance,
Alex.


Top

nubbage
Post subject: Posted: Thu Jul 26, 2007 3:39 am

General


Joined: Fri Feb 17, 2006 12:07 pm
Posts: 218
Location: London UK
Hi Alex
One time I encountered something similar, where a VNA plot turned to rat doo-dooz above a certain frequency, it turned out to be an unexpected resonance. This produced a rapid variation in S parameters around the resonant frequency, and at harmonics of it.
Is there any chance your set-up could exhibit a resonance?





Posted  11/12/2012
Custom Search
More than 10,000 searchable pages indexed.

Your RF Cafe
Progenitor & Webmaster

Click here to read about RF CafeKirt Blattenberger... single-handedly redefining what an engineering website should be.

View the YouTube RF Cafe Intro Video Carpe Diem!
(Seize the Day!)

5th MOB: My USAF radar shop

Airplanes and Rockets: My personal hobby website

Equine Kingdom: My daughter Sally's horse riding website